2025 Kenworth T680 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2025 Kenworth T680 offers a range of transmission options, primarily focusing on automated manual transmissions (AMTs) for optimal efficiency and driver comfort. The specific gear ratios can vary slightly based on the exact transmission model chosen. Below are common configurations you might encounter.

Eaton Endurant XD 18-Speed AMT

PACCAR TX-12 Automated Transmission

Available axle ratios

Kenworth T680 trucks offer a variety of axle ratios to optimize for different applications, from long-haul fuel efficiency to heavy-haul capability.

How to identify your axle ratio

Identifying your Kenworth T680's axle ratio is crucial for proper maintenance and understanding its capabilities. While a door-jamb RPO (Regular Production Option) sticker is common on many vehicles, for heavy-duty trucks like the Kenworth T680, you'll typically find this information on a data plate or sticker located on the axle housing itself, or on a build sheet provided by Kenworth. This sticker will often contain the axle manufacturer (e.g., Dana, Meritor) and the specific ratio. In some cases, a VIN decoder can also provide build information that includes axle ratios, though checking the physical axle tag is usually the most direct method.

Towing vs MPG impact

The choice of axle ratio has a significant impact on your truck's performance. A numerically lower axle ratio (e.g., 2.47 or 2.64) means the driveshaft will spin fewer times for each revolution of the wheels. This results in lower engine RPMs at highway speeds, leading to better fuel economy. However, it also reduces torque multiplication at the wheels, making it less suitable for heavy towing or steep grades.

Conversely, a numerically higher axle ratio (e.g., 3.25 or 3.42) means the driveshaft spins more times for each wheel revolution. This provides greater torque multiplication, which is ideal for heavy towing, hauling large loads, or operating in challenging terrain. The trade-off is higher engine RPMs at highway speeds, which will decrease fuel efficiency.

A balanced ratio like 2.79 or 3.08 often provides a good compromise for general-purpose applications, offering a blend of decent fuel economy and adequate towing capability.

Common issues

While the Kenworth T680 is built for durability, like any heavy-duty component, axle assemblies can experience wear and tear. Common issues include:

• Ring and Pinion Whine: This is often heard as a howling or whining noise that changes with road speed, accelerating and decelerating. It can indicate improper gear mesh, worn gears, or insufficient lubrication.
• Carrier Bearing Wear: The carrier bearings support the differential carrier. Worn bearings can lead to excessive play, vibration, and noise, particularly in turns or when accelerating.
• Limited-Slip Clutch Wear (if equipped): If your T680 is equipped with a limited-slip differential, the clutch packs can wear over time, leading to a loss of the limited-slip function, noticeable as one wheel spinning freely in low-traction situations where both should be driving.

Regular maintenance, including checking fluid levels and quality, can help mitigate these issues.

Find a driveline shop on Repairius.